This invention relates generally to clamping devices for securing an electrical power cable to an electrical junction box to prevent any strain on the cable from being transmitted to its connection to a wiring device.
Electrical power cables are, of course, well known for their use in homes, buildings and other structures to distribute electric power throughout the structure and thereby provide power for lighting, appliances, heating and other similar purposes. Such electrical cables are usually concealed within the walls and ceilings of the structure, with numerous cable segments coupling the various electrical wiring devices (switches, receptacles, etc. housed in outlet boxes) to each other and to the power source.
Because of the number of connections required to couple all of the wiring devices to the source of electrical power, it is important, from the standpoint of safety and reliability, that the connection between each cable segment and any wiring device be made with sufficient strength to prevent separation (or even loosening) of the cable from the wiring device. The need for such strength is particularly important during construction when the cable segments are installed and terminated to the wiring devices. During such installation, the electrician often has to pull on a cable segment, thereby risking disconnection of the other cable end from the wiring device to which it is terminated.
Cable clamps have been developed for insertion in or adjacent cable entry ports in the electrical outlet box containing a wiring device to be connected to an electrical power cable. These cable clamp devices permit the cable to pass into the outlet box for termination to the wiring device, and, once in place, to be secured relative to the outlet box. If a force is then exerted on the cable tending to strain or break the connection with the wiring device, the force is transmitted to and absorbed by the box rather than the electrical connection.
Although these devices provide adequate results in certain applications, they can suffer certain drawbacks. For example, some known clamps (such as shown in U.S. Pat No. 2,973,212) are formed with a lip or jaw for mating with the opening in the box, and include a member made of resilient or spring-like material to permit the clamp to be inserted into the opening with a snap action. Such spring-like structures are subject to deformation if excessive force is applied and are thus capable of providing limited clamping force.
Another common clamp device comprises a bushing insert which has a threaded end adapted to project through a cable entry port. The insert is held in place by a threaded washer screwed onto the threaded end, with a tap screw extending through the insert wall to secure the cable in place after it is installed in place. Thus, the insert requires the additional steps of fully installing the bushing in the opening followed by turning down the screw.
In spite of the long felt need for an economical clamp which can be installed quickly yet is capable of providing substantial clamping strength, no known commercially available clamp adequately meets both criteria.
Accordingly, it is an object of the present invention to provide a new and improved cable clamp member for securing an electrical power cable or tubing to an outlet box or the like. It is also an object of the invention to provide a cable clamp member which is easy to install for minimum installation time yet provides a reliably secure attachment to the box.
Another object of the present invention is to provide a cable clamp member for clamping an electrical cable or tubing to an electrical outlet box or the like, which can be re-used without the risk of weakening or damaging any parts.
The aforementioned problems are overcome, and the foregoing and other objects and advantages are achieved by the cable clamp member of the present invention which is adapted to secure an electrical cable or conduit to a junction box.